Possibly undergassed/losing gas

scotthend

scotthend

Private
Minuteman
Jul 11, 2020
7
1
#1
Had my AR re-barreled with a Faxon Gunner profile 16" with a .625 gas port; mated to a Faxon .625 gas block and mid-length gas tube a few weeks ago. Finally got out to the range today to discover that it wouldn't cycle. It doesn't feel like the bolt is binding in the chamber when working the charging handle and it locks into battery like it should when feeding so my thought is that the gas port may be too small for the length.

Thoughts/possible solutions would be greatly appreciated.

If it makes a difference I was shooting Hornady Black 62gr
 
#2
scotthend said:
Had my AR re-barreled with a Faxon Gunner profile 16" with a .625 gas port; mated to a Faxon .625 gas block and mid-length gas tube a few weeks ago. Finally got out to the range today to discover that it wouldn't cycle. It doesn't feel like the bolt is binding in the chamber when working the charging handle and it locks into battery like it should when feeding so my thought is that the gas port may be too small for the length.

Thoughts/possible solutions would be greatly appreciated.

If it makes a difference I was shooting Hornady Black 62gr
Click to expand...

I 'm sorry, are you saying your gas port measured size is .625 ?

And what gas system length ?
 
#7
scotthend said:
Yes, port is .625 and running a mid length system
Click to expand...
I hope that’s the diameter of the barrel where the gas block sits and not the size of the port.

I would check alignment first, if you need to move the block, slide it off and make sure nothing is blocking the gas port, or gas block.

BCG is good and acti NG like it should? How does the brass look? Any indication that headspace is off? Have you closely inspected for any damage existing or new in the upper/BCG/charging handle?
 
#8
While you have the block off, use a drill bit to determine the size of the gas port hole. Transfer punches, if you have a set and they are small enough, may be better but a drill bit set will do to give you an approximation. That will tell those smarter than I (and those asking about the gas port size) whether there is any concern there, and whether it may need to be opened up.Other than that, make sure everything is well lubed. Doesn’t need to be sloppy, but at least wet. And recheck the gas tube alignment in the upper/gas key for binding when you are checking the gas block/gas port alignment.
 
#9
I had some cycling issues with a brand new WOA barrel and SLR adjustable block until I got some carbon build up under the block. Are you short stroking? Failure to lock back? Failure to feed??
 
#11
If I understand the OP correctly, the gun is a single shot. There is no gas going to the BCG? The BCG is not moving at all? If so, then no gas is being transferred? If that is the case, then there is a complete obstruction in the gas system. Also, I must assume that the OP is not quite understanding the system. I mean no disrespect, however the .625 is the diameter of the gas block. I can guarantee you do not have a gas port that has a diameter of in excess of a 1/2 inch. My understanding is that that barrel has a gas port size in the range of .080. If my assumptions are correct, then the system needs to be disassembled and I am sure the problem will be obvious. Who assembled the rifle? If a gunsmith did, I would take it back.
Some possiblilities:
Gas tube is obstructed or upside down;
Gas block is obstructed or not properly mounted over the gas port;
The barrel gas port is obstructed or not properly placed and drilled.

Just my initial thoughts based on assumptions.

Cheers, Steve
 
#12
ssc45 said:
If I understand the OP correctly, the gun is a single shot. There is no gas going to the BCG? The BCG is not moving at all? If so, then no gas is being transferred? If that is the case, then there is a complete obstruction in the gas system. Also, I must assume that the OP is not quite understanding the system. I mean no disrespect, however the .625 is the diameter of the gas block. I can guarantee you do not have a gas port that has a diameter of in excess of a 1/2 inch. My understanding is that that barrel has a gas port size in the range of .080. If my assumptions are correct, then the system needs to be disassembled and I am sure the problem will be obvious. Who assembled the rifle? If a gunsmith did, I would take it back.
Some possiblilities:
Gas tube is obstructed or upside down;
Gas block is obstructed or not properly mounted over the gas port;
The barrel gas port is obstructed or not properly placed and drilled.

Just my initial thoughts based on assumptions.

Cheers, Steve
Click to expand...
None taken. This is the first time I've ever modified more than the pistol grip or stock. I'm definitely going to break it down and take a look at everything. Referencing what Powder Burns suggested is there a way to ensure everything is lined up after moving the gas block a hair?
 
#13
scotthend said:
None taken. This is the first time I've ever modified more than the pistol grip or stock. I'm definitely going to break it down and take a look at everything. Referencing what Powder Burns suggested is there a way to ensure everything is lined up after moving the gas block a hair?
Click to expand...
Most surefire way, get a pencil and some calipers or a decent ruler. Measure the length of the gas block, measure the distance from the edge of the gas block to the center of the gas port. Mark the barrel with a pencil to correspond with those measurements, make a pencil mark top dead center of the barrel across the gas port location and a pencil mark in the center of the gas block in its front and/or rear edge. Set the gas block on the barrel and make sure all your pencil marks line up. Tighten your bolts and double check nothing shifted. Then wipe your pencil marks off.

The other method, stick an earplug in the chamber and blow compressed air down the muzzle. Move the gas block and align it over the gas port by feeling for air flow out the gas tube.
 
#14
If your barrel is dimpled for a set screw gas block, and assuming the dimple in the barrel and the gas port are in the correct location and the gas block is made correctly, removing the set screw fully and aligning that hole in the gas block with the dimple in the barrel will get your really close. Generally, the hole for the gas in the gas block is big enough to take up any very minor differences in alignment.
 
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#15
The other thing I would advise is- assuming you have an adjustable gas block- is to make sure you understand how it works and make sure it is not fully closed. No movement of the bcg sounds like a bigger issue than poor gas block alignment.
 
#17
Took the handguard off yesterday to start trouble shooting the issue. Using the compressed air technique I couldn't hear anything coming through the gas tube. I loosened the set screws on the block and tried moving it forward a little at a time with no success. Then I notice the gas tube itself looked different than any I'd ever seen over the years of cleaning M16/M4 platforms in the military.

I don't have a punch set (yet) so I went through my drill bits and used the 1/16" and my claw hammer to tap out the roll pin. My suspicion was confirmed when I removed the gas tube to find it had been installed upside down. I wiped it down and reassembled everything and again used the compressed air technique to get it positioned.

Bottom line- if anyone here is in Colorado Springs do NOT go to Oasis

It may be another couple of weeks before I get to the range again but if I have any more issues I'll update again.

Thanks to everyone for your help.
 
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#18
Man, I recently got a completely obstructed gas tube that kept the rifle from cycling at all.

I also got a barrel that had a gas port that was so small it would not cycle ball ammo (.308). After measuring the port and ensuring multiple times that EVERYTHING was properly aligned and that there was no binding issues anywhere I gave up and called the manufacturer. They told me that my port size was proper. My research showed that generally the port should have been larger for that length. I finally drilled out the gas port to what I thought it should have been and surprise! It now works great.

If you have checked absolutely everything for alignment and fit/function, you may have to do the same.

I'm pretty much turned off from large frame ARs now...
 
#19
diggler1833 said:
Man, I recently got a completely obstructed gas tube that kept the rifle from cycling at all.

I also got a barrel that had a gas port that was so small it would not cycle ball ammo (.308). After measuring the port and ensuring multiple times that EVERYTHING was properly aligned and that there was no binding issues anywhere I gave up and called the manufacturer. They told me that my port size was proper. My research showed that generally the port should have been larger for that length. I finally drilled out the gas port to what I thought it should have been and surprise! It now works great.

If you have checked absolutely everything for alignment and fit/function, you may have to do the same.

I'm pretty much turned off from large frame ARs now...
Click to expand...
What size did you drill it out to, and what length gas system are you running? I'm preparing to put a 308 together, and would like to make sure my gas port is good before assembly.
 
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